1. Field of the Disclosure
Exemplary embodiments relate to a display device and, more particularly, to an organic light emitting device.
2. Description of the Related Art
Out of flat panel display devices, a light emitting device is a self-emission display device that does not require a backlight unit and has such characteristics that it can be fabricated to be light and thin, its process can be simplified. Further, the light emitting device can be fabricated at a low temperature, has a high response speed of 1 ms or lower, low power consumption, a wide viewing angle, and high contrast ratio, etc.
In particular, an organic light emitting device includes an emitting layer including an organic material between an anode electrode and a cathode electrode. The organic light emitting device forms an exciton, which is a hole-electron pair, by combining holes received from the anode electrode and electrons received from the cathode electrode inside the organic light-emitting layer, and emits light by energy generated when the exciton returns to a ground level. The organic light emitting display further comprises a hole (electron) injecting layer and/or a hole (electron) transporting layer between the anode or the cathode and the emitting layer.
Because the organic light emitting device includes the emitting layer including the organic material, it is easily degraded when external moisture or oxygen is infiltrated into the display device. Also, as a driving time of the organic light emitting device is lengthened, the emitting layer is readily degraded by heat generated in a driving unit.
In addition, having the semiconductor characteristics, the emitting layer is very sensitive to external temperature. Namely, the amount of current flowing in a light emitting diode changes readily as an ambient temperature goes up or down.
Thus, because the amount of voltage to be applied to obtain the same luminance varies according to a degradation degree or according to the surroundings, the organic light emitting device has disadvantages in that it can hardly provide a uniform quality of screen images.
Therefore, in order to compensate the degradation degree of the organic light emitting device or the voltage value changing according to temperature, monitor pixels are formed at a non-emission area near a display unit.
The monitor pixels include light emitting diodes formed in the same process as that of subpixels of the organic light emitting device and receive direct current (DC) power of a certain magnitude during a certain time. A magnitude of the voltage at the monitor pixels may be measured and provided to the subpixels of the display unit to thus compensate the voltage according to degradation or temperature.
However, measurement of voltage of the monitor pixels is performed while the organic light emitting device is being driven, so a problem arises in that there is a deviation in each size of measured voltages.
In other words, because the signal applied to the monitor pixels is DC power and a data signal applied to the subpixels is an alternating current (AC) signal, a signal interference is caused between lines transferring the DC power to the monitor pixels and lines transferring the data signal to the subpixels positioned to be adjacent to the monitor pixels, resulting in that the size of the measured voltage may be different. Thus, it is difficult to provide an accurate compensation voltage in consideration of the degradation of the subpixels of the display unit and temperature.